Hearing aid



FIG. 1 is a rear view of a hearing aid showing our new design;

FIG. 2 is a left side view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a perspective view thereof.

The broken lines represent unclaimed portions of the hearing aid and form no part of the claimed design. 

CLAIM The ornamental design for a hearing aid, as shown and described. 